1 . Field of the Invention
The present invention relates to an adjustment mechanism for a movable platen used in an injection molding machine.
2 . Description of the Related Art
FIG. 1 is a view showing a mold clamping unit of an injection molding machine. The mold clamping unit comprises a movable platen 30, rear platen 31, toggles 32, fixed platen 33, crosshead 34, and ball screw shaft 38. The rear platen 31 and the fixed platen 33 are connected by a plurality of tie-bars 41, and the movable platen 30 can be advanced (to the right in FIG. 1) toward and retracted (to the left in FIG. 1) from the fixed platen 33 by the toggles 32.
A mold 40 is mounted on the movable platen 30. The position of the movable platen 30 can be changed by advancing or retracting the crosshead 34 on the ball screw shaft 38. If the crosshead 34 is advanced (to the right in FIG. 1), in this case, the movable platen 30 is advanced to close the mold.
In precision molding such as lens molding, the parallelism between the fixed and movable platens greatly affects the quality of molded products. The parallelism in the vertical direction is conventionally adjusted by changing the slant or inclination of the movable platen. In general, the inclination of the movable platen is changed by changing the respective heights of the fixed-platen-side end portion of a support portion between the movable platen and the base frame and the opposite end portion. The heights of the two opposite end portions of the support portion are typically changed by a method using wedges, shims, or bolts.
Japanese Patent Application Laid-Open No. 2009-262514 discloses a technique related to an inclination adjustment method for a movable platen using a bolt-and-wedge assembly. Bolts are used as adjustment elements for adjusting the height of the movable platen above a base of a molding machine. The distal ends of the respective threaded portions of the bolts contact the fixed-platen-side end portion of a support block, which is inserted below the movable platen, and the end portion opposite thereto. Thus, the level of the movable platen in the vertical direction above the base of the molding machine in a position corresponding to each of the bolts can be adjusted by means of a wedge-shaped portion of the support block by rotating the bolts.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2009-262514 described above, a front or rear inclination of the movable platen toward a fixed platen can be adjusted by regulating the vertical positions of the movable platen on the fixed-platen side and the opposite side by means of the wedge-shaped portion of the support block by rotating the bolts. Normally, in this case, the movable platen is designed so that its center of gravity is located at an intermediate point between the positions of contact of the bolts, and the degrees to which the positions are raised are adjusted by the weight of the movable platen. If a mold is mounted on the movable platen, however, the position of the center of gravity may be sometimes changed and shifted from between the positions of contact of the bolts. If the bolts are adjusted in this case, the entire movable platen only moves up and down and its inclination cannot be adjusted, in some cases.